The present invention relates to a system for controlling a light-generating apparatus. The light-generating apparatus envisioned includes a circuit having a power source and a light. For example, the apparatus may constitute an ordinary flashlight, the light may be the flashlight's bulb, and the power source may be one or more batteries removably inserted into the battery compartment of the flashlight.
A problem typically encountered with light-generating apparatus is that shortly after replenishment of the power source, the performance of the power source starts to degrade, and the intensity of the light quickly begins to dim to unacceptable levels. In the case of the ordinary incandescent flashlight bulb, for example, as described in Weber, U.S. Pat. No. 5,821,697 (the “Weber reference”), an objectionable “yellow” light begins to appear with merely a 10–20% decrease in battery voltage. Indeed, as Weber further points out, only a 7% drop in battery voltage causes the bulb to lose 20% of its light output. Broadhurst, U.S. Pat. No. 6,316,880 (the “Broadhurst reference”), suggests that this steep performance decline is an inherent characteristic of the tungsten filament used in incandescent bulbs, which act as a black body radiator producing light proportional to the fourth power of the filament temperature.
The filler gas used in the bulb also affects performance. As described, for example, in Salerno, U.S. Pat. No. 6,246,184 (the “Salerno reference”), a typical xenon-filled flashlight bulb loses 50% of its intensity with only a 20% drop in input voltage. The problem is even more severe with “Krypton” gas-filled bulbs that, as Weber points out, drain the battery relatively more rapidly. Aggravating this problem further is the performance of the typical dry-cell battery under load. As Weber describes, such a battery exhibits three pronounced performance regions: the first during the initial portion of operation where its internal impedance increases rapidly; the second during the middle portion where the internal impedance tends to level off; and the third during the final portion where the impedance again increases rapidly to the point where the battery has no further practical value. Accordingly, designers and operators have faced a trade-off between diminished lighting ability, with attendant frustration and risks, and premature replacement or replenishment of the batteries, with attendant inconvenience, inefficiency, and costs.
To address the foregoing problem, various mechanisms for stabilizing the lamp's intensity have been proposed. One frequently cited design is shown in Mallory, U.S. Pat. No. 4,499,525 (the “Mallory reference”). In the Mallory reference, a lamp of lower voltage rating replaces the lamp originally installed, and a switching element is inserted in the circuit between the power source and the light to enable pulsed operation of the circuit. As the battery voltage declines, this decline is detected through a feedback circuit, and the width of the pulses are increased so as to increase the duty cycle of the pulse train and automatically compensate for the declining voltage.
A related design is shown in Nilssen (FIG. 5), U.S. Pat. No. 5,498,934 (the “Nilssen reference”), where an integrated circuit (IC) performs the switching function and the duty cycle is varied from 100% (with the IC switched out of the circuit) to 50% as based on feedback provided from direct sensing of the light's intensity through a photodetector. A contrasting design is shown in the Weber reference in which, in order to reduce purported circuit inefficiencies and tolerance sensitivities, the switching element is replaced by an active element that continuously adjusts the current level in the circuit in noncyclical or linear fashion. In one variant described in The Weber reference, for example, the current flow is continuously adjusted through a MOSFET in response to changes in voltage detected across the lamp. The common theme in each of these approaches is self-regulation of the lamp's intensity by means of active feedback.
As disclosed in Schmidt et al., U.S. Pat. No. 6,040,660 (the “Schmidt reference”), control devices of the above type have been conveniently packaged in disk-like or flattened form with their external contact points arranged on opposite sides. This enables an existing flashlight or lantern to be retrofitted with the device by simply opening the battery compartment and inserting the device behind the batteries. The device can also be made to be inserted above the batteries in a position proximate the lamp in the manner suggested by the Salerno reference. Still another approach has been to embed the device in a battery of conventional size as suggested in Bruwer, U.S. Pat. No. 6,621,225 (the “Bruwer '225 reference”).
After the light-generating apparatus has been initially switched on, some prior mechanisms provide for a dimming function. Here the intensity of the light is backed off or decreased from its fully lit level in order to provide for variable lighting and to conserve battery and lamp life. Typically, such dimming is controlled by a manual switch, that is, either the switch can be toggled from its normal position to a dimmed position, as indicated by Yee, U.S. Pat. No. 6,160,355 (the “Yee reference”), or the switch is of variable type providing a continuous range of dimming, that is, each different position of the switch corresponds to a unique dimming level, as shown in the Nilssen reference. The variable switch, from a circuit standpoint, represents a variable resistor, and this switch can either be integrated with the primary power switch, as Nilssen shows, or separately provided, as shown in the Broadhurst reference.
Yet another approach to implementing the dimming function is described in the Schmidt reference and the Bruwer '225 reference. Under this approach, after the circuit is initially switched to its fully on position, the primary switch is briefly actuated in accordance with a predefined sequence, such as being switched off and back on again within a predetermined “switch-over” time, to indicate a dimming operation is desired. The dimming interval is set to correspond either to the switch-over interval, that is normally extremely brief because of the need to maintain power to the lamp, or a predetermined time interval following the switch-over interval, in which case the dimming operation proceeds in stages, that is to say, in stepwise fashion. In the Schmidt reference, for example, the first switch actuation signaling dimming reduces the light intensity by 50%, whereas the second such actuation reduces the intensity by another 50% (to one-quarter of the original intensity). Under this approach, it will be noted that discrete switch actions result in discrete dimming operations. Although this approach does not require special modification of the switch, as is frequently the case with a variable switch, “fine-tuning” of the lamp's intensity in the manner offered by the variable switch is not provided.
Another function found in some prior mechanisms is an indicator that signals a weakened condition of the batteries. In the Weber reference and the Yee reference, for example, when the battery voltage reaches some fixed percentage of the rated voltage so as to establish the batteries are near exhaustion, either an indicator LED turns on or a supplemental battery is switched into the primary circuit.
In the Bruwer '225 reference, a “good” battery condition is indicated by an LED briefly flashing every 10 seconds or other interval. As Bruwer explains, this also assists the user in more easily finding the flashlight in the dark. Consistent with this, Bruwer describes how an internal energy storage element, such as a capacitor, can be charged by the battery during the off portion of each switch cycle, so that the switch control has a source of reserve power to continue switching operations even when the battery's available power is primarily being directed to the lamp. This type of intermittent flashing may be contrasted with a more regular flashing routine where, for example, the flashlight is flashed on and off every half second or so. Bruwer also discloses this other type of flashing routine for signaling distress or emergency, as do several others of the references above cited.